Controller and power source for implantable blood pump

ABSTRACT

Methods and apparatus for controlling the operation of, and providing power for and to, implantable ventricular assist devices which include a brushless DC motor-driven blood pump, are disclosed. In one embodiment, a control system for driving an implantable pump is provided. The digital processor is responsive to data associated with the operation of the pump received at the data transfer port, and from the program data stored in memory, (i) to determine therefrom, the identity of the pump, (ii) to determine therefrom, electrical characteristics and features of the identified pump, and (iii) to adaptively generate and apply to the data port, control signals for driving the identified pump. Latch mechanisms, an elongated flexible electrical cable with a strain relief segment, and a lower housing portion that is heavier than an upper housing portion, may also be provided with the control system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/749,038 filed Jan. 4, 2013, thedisclosure of which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to the field of implantable medical devices. Inparticular, this invention is drawn to controllers and power suppliesfor motor-driven implantable medical device applications.

APPLICATIONS INCORPORATED BY REFERENCE

U.S. Patent Publication No. 2012/0226350, titled “Controller and PowerSource for Implantable Blood Pump” is hereby incorporated by referenceherein. U.S. Patent Publication No. 2012/0086402, titled “Fault-TolerantPower Supply” is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

Implantable medical devices, such as ventricular assist devices, arebeing developed for long term treatment of chronic heart failure. Suchdevices require a pumping mechanism to move blood. Due to the nature ofthe application, the pumping mechanism must be highly reliable. Patientcomfort is also a significant consideration.

Electrically powered pumping mechanisms typically rely on a motor suchas a brushless DC motor. Brushless DC motors offer maintenanceadvantages in implant applications due to the lack of wear-pronebrushes. Due to the lack of these electro and mechanical commutationcomponents, commutation is generally provided electrically by driveelectronics.

A prior art HeartWare Ventricular Assist System, manufactured byHeartWare Inc, Framingham Mass., is an example of an implantableventricular assist device. At the core of the HeartWare VentricularAssist System is a small implantable centrifugal blood pump called aHVAD® pump employing a brushless DC motor.

When implanted in a patient in a typical scenario, the pump draws bloodfrom the left ventricle and propels that blood through an outflow graftconnected to the patient's ascending aorta. The device is capable ofgenerating up to 10 liters of blood flow per minute. With a displacedvolume of only 50 cc, the HVAD pump is suitable for implantation in thepericardial space, directly adjacent to the heart Implantation above thediaphragm leads to relatively short surgery time and quick recovery.

The HVAD pump has only one moving part, an impeller, which spins at arate between 1800 and 4000 revolutions per minute. The impeller issuspended within the pump housing through a combination of passivemagnets and hydrodynamic thrust bearings. This hydrodynamic suspensionis achieved by a gentle incline on the upper surfaces of the impellerblades. When the impeller spins, blood flows across these inclinedsurfaces, creating a “cushion” between the impeller and the pumphousing. There are no mechanical bearings or any points of contactbetween the impeller and the pump housing.

Device reliability is enhanced through the use of dual motor statorswith independent drive circuitry, allowing a seamless transition betweendual and single stator mode if required. The pump's inflow cannula isintegrated with the device, and surgically implanted into the heart'sventricle. This proximity is expected to facilitate ease of implant andto help ensure optimal blood flow characteristics. The use of awide-bladed impeller and clear flow paths through the system minimizesrisk of pump-induced hemolysis (damage to blood cells) or thrombus(blood clotting).

Typically, while the pump is implanted in the patient, a controller andthe drive electronics for the pump, and other control subsystems for thepump, including the power supply, are located outside the patient, forexample, in a control/power supply module tethered by a transcutaneouselectrical cable, to the implanted pump of the overall HeartWareVentricular Assist System.

For the HeartWare Ventricular Assist System, an external (to thepatient) controller includes the drive electronics for the pump (coupleddirectly to the windings of the motor) and provides drive and controlsignals to the pump. The controller also provides feedback and alarms tothe patient regarding the operation of the device. Commutation controlfor the brushless DC motors is effected by the controller and the driveelectronics, in a feedback manner. The controller provides a commutationcontrol signal for a selected phase of the motor in accordance with asampled back-emf voltage of that phase (sensed via the tether cable).The back-emf is sampled only while the corresponding selected phasedrive voltage is substantially zero. The frequency of the brushless DCdrive voltage is varied in accordance with the commutation controlsignal. In one form, the back-emf is normalized with respect to acommanded rotor angular velocity. A speed control generates a speedcontrol signal corresponding to a difference between a commanded angularvelocity and an angular velocity inferred from the frequency of thedrive voltage.

A redundant power supply is provided by two batteries, or one batteryand an AC adapter or DC adapter. The redundant power supply providespower for the controller, and particularly the drive electronics. Whenthe battery is depleted (for example, after approximately 6 hours), thecontroller automatically switches to the standby power source, batteryor adapter, and the depleted battery is replaced.

A “Patient Pack” assembly includes a carrying case that holds thecontroller and power source(s). The case can be adapted to be carriedover the patient's shoulder or worn around the patient's waist.

While the prior art HeartWare Ventricular Assist System in theaggregate, performs the desired ventricular assist functions requiredfor long term treatment of chronic heart failure, there is a need forimproved subsystems and subassemblies which would provide enhanced bloodflow results and improved patient-convenience features, easing themaintenance burden on the patient, thereby providing an improved qualityof life.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a control system for driving an implantable bloodpump includes a first housing including electronic components configuredto drive the pump and a second housing including a battery. The firsthousing includes a first latch member extending from the first housingon a first side of the first housing and first and second recesses on asecond side of the first housing. The second housing includes a thirdrecess on a first side of the second housing and second and third latchmembers extending from the second housing on a second side of the secondhousing. When the first side of the first housing is aligned with thefirst side of the second housing, the first latch member aligns with thethird recess, the second latch member aligns with the first recess, andthe third latch member aligns with the second recess. The second andthird latch members may each include bottom connected to the secondhousing and a top curving away from the first side of the secondhousing.

In another embodiment of the invention, a control system for driving animplantable blood pump includes an internal battery, an externalbattery, and a processor configured to perform an estimation of aremaining run time of the internal and external batteries. Theestimation includes determining a remaining capacity of the internalbattery, determining a remaining capacity of the external battery,determining a consumption rate of the internal battery, and determininga consumption rate of the external battery. Determining the remainingcapacity of the external battery includes determining a value of theremaining capacity of the internal battery and modifying the value ofthe remaining capacity of the internal battery to account for a loss inefficiency when the external battery charges the internal battery.

In another embodiment of the invention, a control system for driving animplantable blood pump includes a first housing including electroniccomponents configured to drive the pump, speakers, and a vibratingmechanism. The vibrating mechanism vibrates during a first intervalfollowing the detection of an alarm condition and the speakers sound anaudible alarm during a second interval following the detection of thealarm condition. The first interval precedes the second interval, andthe speakers are silent during the first interval.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be better understood by reference tothe following detailed description when considered in connection withthe accompanying drawings, wherein:

FIG. 1 is front-top-side view of a control system and connecting cableof the disclosure;

FIG. 2 is partially rear-side view of the control system and connectingcable of FIG. 1;

FIGS. 3A-B are side views of the control system and connecting cable ofFIG. 1, showing a battery-containing portion detached from aprocessor-containing portion, and the battery-containing portionattached to the processor-containing portion, respectively;

FIGS. 4A-D show top views of the top panel. with a display devicethereon, of the control system of FIG. 1; and

FIG. 5 is a diagrammatic representation of the control system andconnecting cable of FIG. 1, together with an exemplary pump.

FIGS. 6A-E illustrate multiple views of an alternate embodiment of topand bottom housings of a control system.

DETAILED DESCRIPTION

A control system 10 for controlling the operation of, and providingpower for and to, implantable ventricular assist devices which include apump employing a brushless DC motor-driven blood pump, is shown in FIGS.1-4. The control system 10 is shown in diagrammatic form in FIG. 5,together with an exemplary pump 12.

As shown in FIGS. 1-5, the control system 10 includes a housing 16disposed about an interior region 20. Housing 16 extends along a housingaxis 22 between a top end 16A and a bottom end 16B. At the top end 16A,a top panel 24 having a substantially planar outer surface, extendstransverse to the housing axis 22. At the bottom end 16B, a bottom panel26 having a substantially planar outer surface, extends transverse tothe housing axis 22. Lateral surfaces LS of housing 16 extend betweenthe circumferential outer boundary of top panel 24 and thecircumferential outer boundary of bottom panel 26. In the aggregate, thelateral surfaces of housing 16 form a tube-like structure extendingalong axis 22, with the end panels 24 and 26 forming closures to thetube, or tube-like, structure, enclosing the interior region 20.

The tube-like structure includes a first, or outer, portion 30 (referredto herein as “LS outer portion 30”) opposite to a second, or inner,portion 32 (referred to herein as “LS inner portion 32”). Opposinguppermost portions of the outermost surfaces of LS outer portion 30 andLS inner portion 32 are substantially planar as well as substantiallyparallel, although as illustrated particularly in FIGS. 1-4, thoseportions are not precisely parallel. Different shapes and relationshipsmay be employed in other embodiments.

A first display device 40 is disposed on the outer surface of top panel24. A second display device 42 is disposed on the outer surface of theLS inner portion 32. The second display device 42 is optional and may beomitted from the control system 10. The housing 16 also includes on alateral surface, a power port 46 and a data port 48 disposed within aninput/output (I/O) connector assembly 49. An input device 50 is disposedon the outer surface of LS outer portion 30.

An elongated flexible electrical cable 51 extends from a controller end52 to a pump end 54. The cable 51 further includes a flexible,helical-shaped strain relief segment 55 (shown in FIGS. 1-3) between thecable ends 52 and 54. A controller-end connector assembly 56 is disposedat the controller end 52, and a pump end connector assembly 60 isdisposed at the pump end 54 of cable 51. The connector assembly 56includes connector portions 46′ and 48′ adapted to mate with the powerport 46 and the data port 48, respectively, of the I/O connectorassembly 49.

The pump end connector assembly 60 similarly includes connector portions62′ and 64′ adapted to mate with a pump power port 62 and pump data port64 of a pump I/O connector assembly 68.

The controller-end connector assembly 56 is adapted to mate with an I/Oconnector assembly 49 on the housing 16, and the pump-end connectorassembly 60 is adapted to mate with the pump connector assembly 68 onthe pump 12.

When the controller-end connector assembly 56 is connected to the I/Oconnector assembly 49 of the controller 10, and the pump end connectorassembly 60 is connected to the pump I/O connector assembly 68 of thepump 12, pump drive signals can pass between the power output port 46and the pump power port 62. Data can pass between the data transfer port48 and the pump data port 64, making available to data processor 32, thereal-time impedances of the windings of the motor of pump 12.

In the illustrated embodiment, the housing is split into two opposedcup-like components: cup-like upper housing portion A having acircumferential rim R1, and cup-like lower housing portion B having acircumferential rim R2. Rim R1 of the upper housing portion A is adaptedto interfit with and reversibly couple to the rim R2 of the lowerhousing portion B. A latch assembly enables the quick release of housingportion A from or to lower housing portion B, in response to depressionof a release button RB disposed on the LS outer portion 30 of upperhousing portion A (and an associated latch assembly. not shown). Rim R1and rim R2 are shown in FIG. 1 by the reference symbol “R1/R2”, and inFIG. 5, rim R1 and rim R2 are depicted as adjacent dashed linesextending across housing 16.

In the illustrated embodiment, the cup-like housing portion B provideselectrical power for the operation of control system 10. As shown inFIG. 5, housing portion B includes in its interior, a power supplysupport structure 80. The support structure 80 has a cup-like formadapted to receive a battery 84 in its interior region. In some forms ofthe control system 10, the battery 84 is affixed to housing portion Band the portion B/battery module is replaceable as a unit. In otherforms, the battery 84 is removably located in housing portion B, and isuser-replaceable within housing portion B. In the illustrated form ofFIG. 5, the interior of the power supply support structure 80 isgeometrically keyed to the shape of the battery 84, to aid a user inreplacing the battery in a fail-safe manner In that structure, both thesupport structure 80 and the battery 84 are shown with geometric shapekeying so that the battery 84 can only be inserted in support structure80 in a single, proper manner A secondary, or back-up, battery 88 isdisposed within the interior of upper housing portion A, and is coupledto the various elements in control system 10, to provide back-up powerto control system 10 in the event of catastrophic failure of battery 84or during routine replacement of battery 84 with a charged or freshunit.

As shown in FIG. 5 of the illustrated embodiment, the support structure80 also includes power jack 87 so that the control system 10 can bepowered by an external power source.

In the illustrated embodiment, the cup-like housing portion A houses thecomponents which provide functional operation of control system 10, asit relates to the driving of an implanted pump 12. The housing portion Ahouses a digital signal processor 92 and an associated memory 94, a pumpdrive network 98, and, as noted above the secondary battery 88, as wellas cabling which interconnects the various elements in the controlsystem 10.

An electrical power conductor assembly P is disposed within interiorregion 20. That electrical power conductor assembly P is associated withthe power supply support structure 80, and couples electrical power froma power supply (whether it be from a battery 84 disposed in supportstructure 80, from an external source by way of power jack 87 or fromsecondary battery 88), and provides electrical power to all elements inthe control system 10. In addition, the electrical power conductorassembly P provides a power drive signal line from the digital processor92, by way of a power amplifier 98, to the electrical power output port46, where that power drive signal can be coupled via cable 51 to themotor (not shown) of pump 12.

A data conductor assembly D also is disposed within interior region 20.The data conductor assembly D provides analog “data” representative ofthe current state of the motor of pump 12, received via cable 51 at datatransfer port 48, to the digital processor 92. In one form, that analog“data” is provided as a direct line to the windings of the motor of pump12, from which the digital processor determines the impedance as afunction of time of the respective windings of the motor. In response tothat “impedance” data, the digital processor determines the appropriatedrive power signal to be applied by way of power port 46 and cable 51,to the motor.

The input device 50 in some forms, includes a keyboard, and in otherforms includes a connector, and in still other forms, includes both.Through the input device 50, a user of, or administrator for, thecontrol system 10 can activate or deactivate the system 10, or can add,modify or delete any information associated with the operation of thesystem 10, for example by modifying the information stored in memory 94.

The control system 10 is adapted for use by an ambulatory patient whohas an implanted blood pump. Under control of system 10, the patient'spump performs as programmed. For convenience, the patient can wear thecontrol system 10 in a holster-like support extending about his or herwaist, with the housing axis 22 substantially vertical and the LS innerportion against the patient's body. With this configuration, the patientcan conveniently view the display device 40 on top panel 24, withoutremoving control system 10 from the holster. An administrator, forexample, a physician or nurse, who might hold the system 10 afterremoving it from the patient's holster, can view either display device40 or display device 42 on LS inner portion 32. In the illustrated form,display 42 is relatively large compared to display device 40, so thatmore complex information can be displayed to the administrator whilerelatively simple, albeit highly useful, information can be displayed tothe patient.

The memory 94 stores program information, for example, for controllingthe operation of one of a number of (same or different model)implantable blood pumps which might be connected to, and driven by, thesystem 10. The digital processor 92 is adapted to run and control theoverall system 10 as well as a pump attached thereto via cable 51.Display 42 is driven by the processor 92 to selectively displayinformation which is generally useful to an administrator of a pump 12,such as a nurse or physician. In embodiments with or without the seconddisplay 42, the control system 10 may additionally be connected to amonitor, for example at a hospital or other clinical setting, which maydisplay the type of information displayed on second display 42 orinclude additional, further detailed information that would otherwise bedifficult to display on the second display 42.

In operation, the control system 10, when deployed, is coupled by way ofcable 51 to a pump 12. Pursuant to its supervisory program from thememory 94, the system 10 determines from a coupled pump 12, the identityof the pump, for example the manufacturer and model number, the serialnumber, and in some cases the identity of the patient associated withthe pump. From that determined identity information, system 10determines certain electrical characteristics and features of theidentified pump, and in some cases related to the patient associatedwith the pump. System 10 then adaptively generates and applies by way ofthe power port 46, control signals (e.g. pump drive signals) for drivingthe identified pump 12. As noted above, in the illustrated embodiment,the system 10 effectively monitors in real time, the operation of thepump 12, based on the impedance of the windings of the pump's motor, andgenerates appropriate time-based pump drive signals for application tothose windings, to achieve the performance defined by the pump's program(which may be customized to the patient) stored in memory 94.

In one form, system 10 is adapted to control operation of one of anumber of pumps of the same model, and the program information stored inmemory 94 defines the features and modes of operation of the identifiedpump. In some cases this information is customized on apatient-by-patient basis, for each of a number of prospective pumps. Inanother form, system 10 is adapted to control operation of all of anumber of different types of pumps. Similar control information isprovided for each such pump in memory 94. In some cases, the pumps to becontrolled are relatively passive, and provide information back to thecontrol system 10 in the form of signal lines coupled to the windings ofthe pump motor, so that impedances can be detected and drive signalsgenerated accordingly. In other cases, the pumps to be controlled areactive, and provide over data port 48, data representative of variousconditions in the pump, for example, identified faults, or datarepresentative of certain conditions, such as indications of theoccurrence of bases for an imminent failure of the pump. Among thevarious determinations made, system 10 generates a signal representativeof the time remaining of operation under battery power, for the specificbattery then installed, taking into consideration of the current stateof charge and expected load/current drawdown. That time-remaining signalis selectively displayed on one, or both, of display devices 40 and 42in human-readable form. The time-remaining value is based in part on thedrive program associated with the pump, so as to provide a highlyaccurate reading all of the time remaining. When the time-remainingvalue reaches a threshold or range indicative of danger to the patient,an alarm is generated, for example, an audible alarm, a vibratory alarm,and a light alarm, solid or flashing.

As noted above, the battery-containing lower cup-like portion B ofhousing 16 can be separated from the upper cup-like portion A (bydepressing button RB), and a replacement lower cup-portion B with afresh, fully charged battery, can replace the removed portion. A sideview of the control system 10 is shown in FIG. 3A (with lower portion Bof housing 16 attached to upper portion A of housing 16) and FIG. 3B(with lower portion B removed and displaced from upper portion A.

Also included within the housing 16, is a wireless transmitter/receiverTX/RX. A transmitter is coupled to the digital processor 92 and isadapted to selectively transmit and receive data. By way of example, thetransmitted data may be representative of indicia of operation of a pump12 under the control of system 10, to a main processor. The informationcan be selected to include data representative of broad aspects of theoperation of the connected pump, such as pump activity, faultconditions, warning/alarm conditions and other data necessary forcomprehensive logs for the pump. The received data, by way of example,may be program or control instructions, or modifications, for use in thecontrol of system 10, and in turn, a pump attached thereto. In variousforms, the control system 10 may include only a transmitter, or only areceiver, rather than the transmitter/receiver in the illustratedembodiment. In other embodiments, the data transfer may be accomplishedvia a wired line. This, for example, may be used when attaching thecontrol system 10 to a hospital monitor to display highly detailedinformation stored on the control system 10.

An exemplary set of information displayed on display device 42, is shownin FIG. 2. The data shown primarily in the form of icons or indicia.Indicia representative of length of time remaining for operation at thecurrent state of battery 84 (7 hours, 35 min), battery life,characteristics of the pump attached to the system 10 (power beingdissipated,=3.4 Watts, pump impeller rotational rate=22000 RPM, and pumpoutput flow rate (6.3 Liters per minute), are all illustrated in FIG. 2.In addition, there is an icon overlying a membrane switch that can bringup data representative of signal strength relevant to the receiver RX,an icon in the shape of a telephone handset overlying a membrane switchthat can initiate a telephone call, an icon in the shape of a wrenchwhich overlying a membrane switch that can initiate a tool or settingscreen, and an icon in the shape of loudspeaker overlying a membraneswitch that can bring up an audio volume control screen. In addition,there is a condition (of control system 10) indicator, which in FIG. 2is a heart-shaped icon that is indicative of “proper operation” of thepump of a patient connected to the system to. An alternative icon forthe condition indicator is shown in FIG. 4D. The aforementioned datadisplayed on display device 42 is primarily of value to anadministrator, such as a physician or nurse.

An exemplary set of information displayed on display device 40, is shownin FIGS. 4A-D. The data shown in FIGS. 4A-B and 40 is in the form ofindicia representative of length of time remaining for operation at thecurrent state of battery 84, battery life, and characteristics of thepump attached to the system 10 (power being dissipated, pump impellerrotational rate, pump output flow rate). There also is aloudspeaker-shaped icon indicative of auditory alarms being on or off(where an “X” overlays the loudspeaker-shaped icon when alarms are“muted temporarily”). As in the illustrated display device 42 in FIG. 2,there also is an icon that is indicative of “proper operation” of thepump of a patient connected to the system 10. In FIGS. 4A-B, that iconis heart-shaped, indicating “proper operation”, or “situation good”, ofthe pump of a patient connected to the system 10. In FIG. 4D, thecondition indicator icon is in the form of the international trafficsignal for “attention”, a triangle with an exclamation point in itsinterior. The data in display device in FIG. 4A is representative of“all is well”, and has a white or blue backlight. The data in displaydevice in FIG. 4B is representative of “alert condition,” and has ayellow backlight. When control system 10 is in its “alarm condition,”the display 40 alternates with that shown in FIG. 4B and that shown inFIG. 4C, with the latter displaying “PRESS SCREEN TO MUTE ALARM,” with ayellow backlight. The data in display device in FIG. 4D isrepresentative of “Situation requires immediate attention,” and has ared backlight.

The backlight values (blue/white, yellow, red) are qualitativeindicators of great importance to the user/patient having his or herimplanted blood pump under the control of the control system 10.

As described above, system 10 is capable of generating a signalrepresentative of the time remaining of operation under battery power,for the specific battery then installed, taking into consideration ofthe current state of charge and expected load/current drawdown. Thesystem 10 uses a runtime estimation algorithm to estimate the remainingruntime, or “Predicted Runtime,” of both the external battery 84 andinternal battery 88. The runtime estimation algorithm for both batteries84, 88 may be periodically executed to determine the Predicted Runtimeof each battery. Generally, Predicted Runtime is estimated as the ratioof the remaining battery capacity, or “Battery Capacity,” to the rate ofbattery consumption, or “Consumption Rate.” Stated otherwise, PredictedRuntime =Battery Capacity/Consumption Rate.

The internal battery 88 may include a battery management system (BMS)chip which may directly provide the remaining capacity of the internalbattery 88. When the runtime estimation algorithm for the internalbattery 88 is initiated, the value for Battery Capacity is equated tothe remaining capacity provided by the BMS chip.

The external battery 84 may also include a BMS chip which may directlyprovide the remaining capacity of the external battery 84. However, forthe external battery 84, the runtime estimation algorithm also takesinto account the capacity of the external battery 84 to transfer chargeto the internal battery 88, as well as efficiency losses and losses inthe boost stage, when determining Battery Capacity. The capacity for theexternal battery 84 to transfer charge to the internal battery 88 isequated to the remaining capacity of the internal battery 88, providedby the BMS chip of the internal battery 88. This value may be modifiedwith a Loss Coefficient to account for loss of capacity when charge istransferred from the external battery 84 to the internal battery 88. Onesuch loss in efficiency may result from the boost circuit used incharging the batteries. For example, the algorithm may assume a 10% lossof capacity during transfer from the external battery 84 to the internalbattery 88. If assuming a 10% loss of capacity, the capacity of theexternal battery 84 to transfer charge to the internal battery 88 wouldbe calculated as the value of Battery Capacity for the internal battery88 multiplied by the Loss Coefficient, in this case 1.1. Thus, the valuefor Battery Capacity of the external battery 84 is calculated as thedifference between the remaining capacity of the external battery 84, asprovided by the BMS chip of the external battery 84, and the capacity totransfer charge to the internal battery 88, as modified by a LossCoefficient. Stated otherwise, External Battery Capacity=LossCoefficient*Internal Battery Capacity.

The value determined for Consumption Rate at any given point may bedetermined by one of at least three different methods. The first methodcalculates an instantaneous consumption rate, determined as the productof average current and voltage of the battery. This first method may beused when certain conditions are met. For example, the first method maybe used when (1) the internal battery 88 is not charging (i.e. it iseither discharging or idle); (2) no AC power adapters are connected tothe system 10; (3) the pump 12 is running; and (4) power is beingprovided to the system from the battery.

The second method for determining Consumption Rate is used when one ofthe conditions described with the first method is not satisfied. Thesecond method entails using the most recently stored value calculatedaccording to the first method. This second method, for example, preventsthe Consumption Rate as being defined as 0 or another artificially smallnumber when the pump has periodically stopped. If the first method wasused when the pump had periodically stopped and there was anartificially low Consumption Rate, the value of Run Time would becalculated as an artificially high value. This artificially lowConsumption Rate would not be expected to continue for the foreseeablefuture, as the pump would realistically start pumping again. Similarconcerns arise for the other conditions described above. If theConsumption Rate is calculated according to the second method with boththe internal battery 88 and external battery 84 connected, the value forConsumption Rate is used for the stored Consumption Rate of bothbatteries. If it is calculated only with the internal battery 88connected, the value is used for the stored Consumption Rate of theinternal battery 88 only.

If the system 10 is in an initialization phase, wherein no ConsumptionRate has been stored according to the first method, and conditions forcalculating the Consumption Rate according to the first method are notsatisfied, a third method may be used. In the third method, a table ofvalues is stored in memory to estimate the Consumption Rate based on theRPM of the pump 12 and a hematocrit setting previously entered by a useror administrator.

The Predicted Runtime calculated based on the determined values ofBattery Capacity and Consumption Rate may then be digitally filtered. Ina preferred embodiment, the filter used is a low pass infinite impulseresponse filter.

After filtering, the Predicted Runtime may then be discretized atdifferent levels based on the magnitude of the Predicted Runtime. Forexample, if the Predicted Runtime is greater than 6 hours, the PredictedRuntime may be reported in increments of 30 minutes. As another example,if the Predicted Runtime is between 3.5 hours and 6 hours, the PredictedRuntime may be reported in increments of 15 minutes. Similarly, if thePredicted Runtime is between 1.5 hours and 3.5 hours, the PredictedRuntime may be reported in increments of 5 minutes. Further, if thePredicted Runtime is less than 1.5 hours, the Predicted Runtime may bereported in increments of 1 minute. For example, if the PredictedRuntime is calculated as 1.88 hours (1 hour and 52 8 minutes), it may bediscretized such that the display reads a battery life of 1 hour and 50minutes. The rationale is that, if the Predicted Runtime iscomparatively long, it is less critical that the user know veryprecisely the amount of battery life remaining before requiringrecharging or replacement of the battery. Contrariwise, if the PredictedRuntime is comparatively short, it is more critical that the user knowvery precisely the amount of battery life remaining before requiringrecharging or replacing the battery. In one embodiment, thediscretization algorithm always occurs downward, such that thediscretized Predicted Runtime is always less than the calculatedPredicted Runtime. The rationale for this embodiment is that it isbetter to provide the user with an underestimate of Predicted Runtimethan an overestimate of Predicted Runtime.

As described above, an elongated flexible electrical cable 51 extendsfrom a controller end 52 to a pump end 54 and includes a flexible,helical-shaped strain relief segment 55 (shown in FIGS. 1-3) between thecable ends 52 and 54. As one cable end 54 remains within the body whenthe pump 12 is implanted in the body while the other cable end 52 isoutside the body connected to the control system 10, a portion of cable51 extends through the patient's skin. The strain relief segment 55 ispositioned outside the body. If the control system 10 is moved farenough away from the body, the relief segment 55 begins to unwind. Byvirtue of the relief segment 55 unwinding, the cable 51 does notsignificantly pull on the body site through which the cable 51 extends.If the cable 51 had no relief segment 55, tension on the cable 51 woulddirectly translate to tension at the body site through which the cable51 extends, or ultimately on the point of connection of the cable 51 tothe pump 12. Avoiding such tension on the portion of the body throughwhich the cable 51 extends also reduces irritation on the skin andpromotes healing of the skin site through which the cable 51 extends.Additionally, the strain relief segment 55 may be calibrated such thatif the control system 10 is dropped by the patient, the strain reliefsegment 55 will uncoil such that the control system 10 contacts theground prior to the strain relief segment 55 fully uncoiling. Thisfunctions to reduce the likelihood that, if the control system 10 isdropped, the weight of the control system 10 will result in componentsof the pump 12 or cable 51 within the body causing internal bodily harm.In one example, the strain relief segment 55 uncoils or unwinds to alength of approximately 2 feet (0.610 meters) while the remainder of thecable 51 positioned outside the body is between approximately 18 inches(0.457 meters) and 2 feet (0.610 meters). In this embodiment, the totallength of the cable 51, when the strain relief segment 55 is uncoiled orunwound, is between approximately 3.5 feet (1.067 meters) and 4 feet(1.219 meters). As the cable 51 usually exits the body near the lowerabdomen area, the total length of the cable 51 outside of the body isenough for the control system 10 to reach the ground when the strainrelief segment 55 is uncoiled.

In addition, as described above, cup-like lower housing portion B mayadapted to receive a battery 84 in its interior region. Normally, thebattery 84 is built into the housing B. The lower housing portion B,including its components, preferably is heavier than the upper housingportion A such that the center of gravity for the control system 10 issituated within the lower housing portion B. This may be accomplished byvirtue of the weight of the battery 84 alone. Alternately, the lowerhousing portion B may be formed of heavier materials or may includeadditional material, such as weighted plates, to lower the center ofgravity of the control system 10. Because the assembly of lower housingB and upper housing A has a low center of gravity, if the control system10 is dropped, the lower housing portion B will be more likely to makeinitial contact with the ground. This may be beneficial in that theupper housing portion A, which houses the electronics to control thepump 12, is less likely to be damaged if the control system 10 isdropped and impacts the floor.

Still further, as described above, certain conditions of the controlsystem 10, such as a low battery condition, may generate an alarmcondition, for example by sounding an audible alarm or causingvibrations of the control system 10. In one embodiment, audible alarmsare used in combination with vibratory alarms. In a further embodiment,the audible and vibratory alarms are staged in sequential phases. Forexample, as an operating condition is reached that causes the controlsystem 10 to alert the user, a first stage vibratory alarm may begenerated. Following a certain period of time, on the order of seconds,a second stage audible alarm may sound in addition to, or to replace,the vibratory alarm. The benefit of such a staged alarm configuration isthat the vibratory alarm gives the patient a first notice of the alarmcondition, upon which the user may act to temporarily mute upcomingaudible alarms. This may be particularly beneficial if the user does notwant to call attention to himself. Since it is generally imperative thata user become aware of an alarm condition in such a control system 10,it may be imprudent to set an alarm to solely a vibratory function, as auser may be more likely to fail to notice if a vibratory alarm isoccurring. By allowing a staged alarm configuration, the user is given afirst chance to privately notice and temporarily disable an alertnotice. If the first vibratory alarm is overlooked, however, the controlsystem 10 will produce a more noticeable audible alarm to increase thelikelihood of the user becoming aware of the alarm condition.

As described above, an embodiment of the control system 10 includes aninternal battery 88 and an external battery 84. An AC or DC poweradapter may also be coupled to the control system to provide power. Inone embodiment the external battery 84 may be removed from the controlsystem 10 when the external battery 84 is low on charge and connected toa charging station to recharge the external battery 84. Alternatively,or in addition, the external battery 84, while connected to the controlsystem 10, may be charged by the control system 10, while the controlsystem 10 itself is being powered by a power adapter. This may bepossible, for example, by a regulating circuit within the control system10 that dictates the supply of power based on a set of hierarchy rules.In the hierarchy rules, if a power adapter is connected to the controlsystem 10 while the external battery 84 is also connected, the controlsystem directs the power to the external battery 84, the internalbattery 88, and the pump 12. If the external battery 84 is not connectedto the control system 10 but the power adapter is connected to thecontrol system 10, the control system directs power to the internalbattery 88 and the pump 12. If the power adapter is not connected to thecontrol system 10, the control system 10 directs the external battery84, if connected, to deliver power to the internal battery 88 and thepump 12. If neither the external battery 84 nor the power adapter isconnected to the control system 10, only the internal battery 88 remainsto power the control system 10 and pump 12.

An alternate embodiment of the control system housing 16′ is illustratedin FIGS. 6A-E. In this embodiment, housing 16′ includes upper housing16A′ and lower housing 16B′. Lower housing 16B′ may accept a battery ina single configuration keyed to the shape of the lower housing 16B′, oralternatively the lower housing 16B′ may be integral with the battery,the battery and lower housing 16B′ being provided as a unit. Many of thefeatures of the housing 16′ are similar or identical to featuresdescribed in relation to housing 16 above. The illustrated embodiment ofhousing 16′, however, includes an integrated latching mechanism to latchthe battery/lower housing 16B′ to the upper housing 16A′. Asillustrated, battery/lower housing 16B′ includes two latches 110extending from an upper surface of the battery/lower housing 16B′. Eachlatch extends upwards and hooks back, away from the center ofbattery/lower housing 16B′. Near the center of the top of battery/lowerhousing 16B′ is a recessed area 120, which may be generally rectangular.Within the recessed area 120 extend connecting pins 130, which allowelectrical connection between the battery/lower housing 16B′ andcomponents of the upper housing 16N. The battery/lower housing 16B mayalso include a plate 140 with recess 150 located on the opposite side ofthe latches 110. The plate 140 may be positioned lower than the topsurface of the battery/lower housing 16B′.

The bottom surface of upper housing 16A′, the details of which are bestillustrated in FIGS. 6D-E, includes features complementary to those ofthe battery/lower housing 16B′. For example, upper housing 16A′ includestwo generally rectangular recesses 115 configured to receive latches 110of the battery/lower housing 16B′. Each latch 110 may be inserted into arespective recess 115, and as the upper housing 16A′ is brought intocontact with battery/lower housing 16B′, the hooked shape of the latches115 helps secure the housing 16′ together.

The upper housing 16A′ also may include a generally rectangularprotrusion 125 near the center of the bottom of upper housing 16A′,configured to fit within the recess 120 of battery/lower housing 16B′.Within a recessed area of the rectangular protrusion 125 of the upperhousing 16A′ are a set of connecting pins 135, which are configured tomate with the connecting pins 130 of the battery/lower housing 16B′ toelectrically connect the housing portions. After the latches 110 areinserted into the recesses 115 and the upper housing 16A′ is rotatedtoward the battery/lower housing 16B′, the rectangular protrusion 125 ofthe upper housing 16A′ enters the rectangular recess 120 of thebattery/lower housing 16B′, after which the connecting pins 130, 135mate with each other and electrically connect the housing.

The upper housing 16A′ may further include a plate 145 and a latch 155protruding through the plate, the plate 145 and latch 155 beingpositioned opposite the recesses 115. When connecting the upper housing16A′ to the battery/lower housing 16B′, after the latches 110 mate withthe recesses 115, and after the connecting pins 130, 135 mate with eachother, the upper housing 16N continues rotation toward the battery/lowerhousing 16B′. As this motion continues, the latch 155 of upper housing16N enters the recess 150 of battery/lower housing 16B′ as the plates140, 145 make contact. This final latching action fully secures theupper housing 16A′ to the battery/lower housing 1613′. As describedabove, the upper housing 16A′ may include a release button RB′. If auser desires to disconnected the upper housing 16A′ form thebattery/lower housing 16B′, he depresses the release button RB′. Oncedepressed, the latch 155 is unlocked from the recess 150, and the upperhousing 16A′ may be disconnected from the battery/lower housing 16B′ insubstantially the reverse order described above relating to connectingthe upper housing 16N with battery/lower housing 16B′.

Additionally, the bottom surface of upper housing 16A′ may include aheat sink 200, for example comprising a material with good heat transferproperties. Such a heat sink 200 helps the control system 10 disperseheat generated during operation of the control system 10. A gasket 300(illustrated in FIG. 6B), may also be provided between the upper housing16A′ and lower housing 16B′ to help prevent water from entering thespace between the upper housing 16A′ and lower housing 16B′ Importantly,the gasket 300 helps exclude water from the connector pins 130, 135,through which electricity flows.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1-18. (canceled)
 19. A control system for driving an implantable bloodpump in a patient comprising: a housing including electronic componentsconfigured to drive the pump; and an elongated flexible electrical cablehaving a first end, a second end remote from the first end, an internalportion, and an external portion, the first end configured to connect tothe housing, the second end configured to operatively connect to theimplantable blood pump, the internal portion configured to be positionedinternal to the patient, and the external portion configured to bepositioned external to the patient; wherein a dynamic member of theexternal portion of the cable has an unstrained condition in which theexternal portion of the cable has a first length, and a strainedcondition in which the external portion of the cable has a secondlength, the second length being between about 3.5 feet and about 4 feetand being greater than the first length.
 20. The control system of claim19, wherein the dynamic member of the cable comprises a strain reliefsegment.
 21. The control system of claim 19, wherein the dynamic memberof the cable has a helical shape when in the unstrained condition. 22.The control system of claim 19, wherein the dynamic member of the cablehas a length of about 2 feet when in the strained condition.
 23. Thecontrol system of claim 19, wherein the external portion of the cableincludes a static member having a length of between about 1.5 feet andabout 2 feet.
 24. The control system of claim 23, wherein the staticmember of the cable includes at least two discontinuous parts.
 25. Thecontrol system of claim 24, wherein the dynamic member of the cable ispositioned between the at least two discontinuous parts of the staticmember of the cable.
 26. The control system of claim 19, wherein thehousing includes a first housing portion that includes the electroniccomponents, and a second housing portion configured to house a battery.27. The control system of claim 26, wherein the first end of the cableis configured to connect to the first housing portion.
 28. The controlsystem of claim 26, wherein the first housing portion includes a firstlatch configured to couple to a corresponding first recess in the secondhousing portion, and the second housing portion includes a second latchconfigured to couple to a corresponding second recess in the firsthousing portion.
 29. A surgical method comprising: implanting a bloodpump into a patient; coupling a first end of an elongated flexibleelectrical cable to a housing of a control system, the control systemconfigured to drive the pump; and operatively coupling a second end ofthe cable to the blood pump; wherein after coupling the first end of thecable to the housing and the second end of the cable to the blood pump,a portion of the cable external to the patient includes a dynamic memberhaving an unstrained condition in which the external portion of thecable has a first length, and a strained condition in which the externalportion of the cable has a second length, the second length beingbetween about 3.5 feet and about 4 feet and being greater than the firstlength.
 30. The method of claim 29, wherein the dynamic member of thecable comprises a strain relief segment.
 31. The method of claim 29,wherein the dynamic member of the cable has a helical shape when in theunstrained condition.
 32. The method of claim 29, wherein the dynamicmember of the cable has a length of about 2 feet when in the strainedcondition.
 33. The method of claim 29, wherein the external portion ofthe cable includes a static member having a length of between about 1.5feet and about 2 feet.
 34. The method of claim 29, wherein the staticmember of the cable includes at least two discontinuous parts.
 35. Themethod of claim 34, wherein the dynamic member of the cable ispositioned between the at least two discontinuous parts of the staticmember of the cable.
 36. The method of claim 29, wherein the housingincludes a first housing portion that includes the electroniccomponents, and a second housing portion configured to house a battery.37. The method of claim 36, wherein the step of connecting the first endof the cable to the housing includes connecting the first end of thecable to the first housing portion.
 38. The method of claim 36, whereinthe first housing portion includes a first latch configured to couple toa corresponding first recess in the second housing portion, and thesecond housing portion includes a second latch configured to couple to acorresponding second recess in the first housing portion.